Abstract: Human activities often impact marine ecosystems. Industrial activities, ports and urbanization in coastal areas are major sources of pollution. Heavy metals are one of the most important pollutants in marine environments. Metals can be toxic to many organisms and accumulate along trophic chains. Monitoring programs of the contaminated regions are important in order to mitigate the consequences of pollution. Chemical, environmental and toxicological analyzes together provide results indicating contamination levels close to the reality of the sites. The analysis of biomonitors can provide information on the bioavailable concentrations of the pollutants, and bioassays can demonstrate results of contaminants in organisms that are rarely observed in the field. Mixing the former tools is more effective to the evaluation of the environmental quality. When the biomonitors are biological substrates, the composition of fauna can be assessed for environmental site analysis. This project aims to analyze the Sargassum algae as a biomotor of heavy metals in a contaminated site and verify if the presence of heavy metals could influence the distribution of fauna, especially herbivores. In addition, toxicological bioassays were used for assess effects of diet spiked with copper on the herbivore amphipod Cymadusa filosa. The seaweed Sargassum from Enseada do Flamengo, Ubatuba, showed a contamination of copper in their tissues comparable to other locations, and thus it can be used as a biomonitor. The local with copper higher contamination in Sargassum also presented a Ampithoidae composition very different from the others. Thereby, the contamination can be a factor affecting the distribution of herbivore amphipods. The results of the bioassays with diet spiked with copper and Cymadusa filosa indicated that it can interfere in sexual development of males, such as the development of the second pair of gnatopods. In addition, we observed a decrease in survival and in the fertility of the females. These results reinforce the importance of integration tools for assessing the quality of marine environments and the feed contamination as an important pathway of heavy metals for these organisms